The Fontan or Fontan/Kreutzer procedure is a palliative (not curative) surgical procedure used to ameliorate complex congenital heart defects, especially in the young. Exemplary heart defects addressed by the Fontan procedure include heart valve defects (tricuspid atresia, pulmonary atresia), abnormalities in pumping ability of the heart (hypoplastic left heart syndrome, hypoplastic right heart syndrome), and other complex congenital heart diseases where a bi-ventricular repair is not possible or contra-indicated (double inlet left ventricle, hetertaxy defects, double outlet right ventricle, etc.). The process was initially described as a surgical treatment for tricuspid atresia.
As a result of the Fontan procedure, a surgically created junction is provided between the superior and inferior vena cava and the pulmonary artery, and venous blood flow is diverted from the superior and inferior vena cava directly to the pulmonary artery, bypassing the right ventricle of the heart. Following the procedure, oxygen-poor blood from the upper and lower body flows through the lungs without being pumped by the heart. Rather, the blood flow into the lungs is driven only by central venous blood pressure. This corrects hypoxia, and leaves a single heart ventricle responsible only for supplying blood to the body.
However, disadvantages and post-surgical complications are associated with the Fontan procedure. In the short term, pleural effusions (fluid build-up around the lungs) can occur, requiring additional surgical interventions. In the long term, atrial scarring may be associated with atrial flutter and atrial fibrillation, also requiring additional surgical intervention. Other long-term risks may be associated with the procedure, such as protein-losing enteropathy and chronic renal insufficiency, although these latter risks are not yet fully quantified.
Also, a high central venous pressure is required to provide a satisfactory supply of blood to the lungs after the Fontan procedure. Immediately or even 2-5 years following the procedure, it is known that the surgically created Fontan circulation often fails due to that high venous pressure required to drive pulmonary circulation. Long term mortality following the Fontan procedure can be as high as 29.1%, characterized by catastrophic failure of circulation and death. The expected event-free survival rate following the Fontan procedure at one, ten, and twenty-five years following the procedure is 80.1%, 74.8%, and 53.6%, respectively. A bi-modal age distribution has been observed in failing Fontan circulation. In early post-operative cases of failing Fontan circulation, the Fontan connection must be surgically taken down. In later post-operative cases, often the only remedy is heart transplantation.
Because of the above complications, in cases of failing Fontan circulation cavopulmonary assistance is often indicated, to actively move blood from the superior/inferior vena cava into pulmonary circulation, to decrease the central venous pressure required to provide the needed flow of blood to the lungs, and to reverse the pathophysiology associated with failing Fontan circulation. Attempts have been made to alleviate failing Fontan circulation by implanting a right ventricular assist device (RVAD). However, this requires a traumatic surgical intervention to implate the device, and also requires take-down of the Fontan connection to allow pump installation. Dual hemopumps have been evaluated to restore or assist failing Fontan circulation. However, in such cases using two hemopumps, two surgical site cannulations are required, which is unduly traumatic to a patient. Also, patient mobility is severely restricted when two pumps must be deployed by cannulation.
A number of smaller pumps have been evaluated, but most require two pumping mechanisms for deployment in the superior and inferior vena cava (above and below the surgically created Fontan connection) to move blood toward and into pulmonary circulation. Because of the dual pumps/dual cannulations required, such pumps cannot be made ambulatory, i.e. the patient must be substantially bedridden after deployment of the pumps. Single pump mechanisms have been evaluated. Such pumps can create the required flow of blood into the pulmonary artery, but are difficult to deploy and consistently maintain in position due to the need for precise placement at the Fontan anastomosis surgically created at the juncture of the superior/inferior vena cava and the pulmonary artery. Proper alignment of this type of pump at the pulmonary artery and retaining that proper alignment is difficult to impossible, even with patient sedation, and further because of the difficulting in maintaining proper positioning after deployment, such pumps cannot be made ambulatory. Still other single pump mechanisms considered require surgical creation of an offset between the superior and inferior vena cava to promote blood flow into the pulmonary artery, increasing surgical difficulty and resultant complications for the patient.
There is accordingly a need in the art for improvements to pumps for cavopulmonary assistance in the event of failing Fontan circulation. Such improved pumps should require only a single pump mechanism requiring only one cannulation, but should still create satisfactory blood flow from both the superior and inferior vena cava into the pulmonary artery. Moreover, the pump should be relatively simple to deploy at the surgically created Fontan connection site, should not require absolutely precise placement to provide proper pump operation and blood flow, and should allow for a degree of displacement after deployment without affecting proper pump operation and blood flow. Still more, the pump should be ambulatory, allowing patient mobility and improved comfort after the procedure.